The term “fluid” relates generally to a gas, a liquid or a flowable phase mixture consisting of gaseous, liquid and/or solid constituents. The term “component” refers here generally to a separable proportion of the multi-component fluid with specific chemical and/or physical properties, on the basis of which this component can be distinguished from at least one further component of the multi-component fluid. The components of the multi-component fluid are formed here in particular by different chemical substances. In principle, a component of the multi-component fluid may however also already be formed itself from a mixture of different chemical substances. Similarly, different phases (states of aggregation) of the same chemical substance or of the same chemical substance mixture may form different components of the multi-component fluid. That component of which the mass proportion is to be determined according to the method is also referred to hereinafter—to distinguish terminologically from further components of the multi-component fluid—as the “first component”.
The multi-component fluid is in particular a synthesis gas, as is used for example as a fuel gas for combustion in power plant gas turbines. Such a synthesis gas usually consists of hydrogen (H2), carbon monoxide (CO), carbon dioxide (CO2), nitrogen (N2) and water (H2O). The water content is usually varied, for example by means of mixing in steam, in order to set the reactivity of the combustion gas such that required emission limits (for example with regard to the nitrous oxide (NOx) output) are maintained. The water content of a typical synthesis gas may reach or exceed 50%.
In the combustion of a synthesis gas in a power plant gas turbine, a real-time gas analysis is desirable, since the gas composition, and consequently the variables that are important for the combustion in the gas turbine (for example the Wobbe index and the reactivity), are subject to variations over time that are due to the gasification process and are caused for example by changing process conditions or starting materials.
On account of the high combustion gas temperatures in the range of approximately 200° Celsius and the high proportion of water of customary synthesis gases, commonly used methods for gas analysis, in particular infrared absorption measurement and gas chromatography, cannot be applied directly to the combustion gas. Rather, before such a gas analysis is applied, generally a drying and cooling of the combustion gas is required. However, this cooling and drying process already leads disadvantageously to a considerable falsification of the original gas composition, especially since a considerable part of the water originally contained in the synthesis gas is removed.
DE 44 33 451 A1 discloses a method for determining the water content in a gas in which the volumetric flow or mass flow of the gas to be analyzed is determined by measuring the differential pressure falling across a flow resistance. Following this measurement, the water contained in the gas is removed at least for the most part in a separation step by condensation. After the separation step, the mass flow or volumetric flow of the dried gas resulting from the separation step is determined. This measurement in turn takes place indirectly by way of the differential pressure falling across a flow resistance. The mass proportion of the water originally contained in the gas is deduced here from the difference in the measured mass flow or volumetric flows. The residual moisture of the dried gas is taken into account here as a correction factor. The dried and cooled gas can be subsequently fed to a gas analysis system.
U.S. Pat. No. 5,050,109 A also discloses a method and a device for determining the humidity of ambient air surrounding an aircraft in flight. In this method, moisture is separated from a captured flow of ambient air in a water separator. The respective mass flow, at least of the flow of air fed to the water separator and of the moisture discharged from the water separator, are measured. The humidity of the ambient air is calculated from the measured mass flow values, while additionally taking into account the efficiency of the water separator.
Finally, US 2003/0136185 A1 discloses a method and a device for determining the volumetric flow rate in a three-phase mixure of water, oil and gas. In this method, a predominantly gaseous component and a predominantly liquid component are separated from the three-phase mixture in a separator, the predominantly liquid component containing a proportion of water and a proportion of oil. The density of the predominantly liquid component is determined by means of a Coriolis flowmeter. Furthermore, the relative proportion of water of the predominantly liquid component is determined by means of a hydrometer. The density and the relative proportion of water of the predominantly liquid component are in this case determined at a point in time at which the predominantly liquid component is substantially free of entrained gas.